Generally, in managing an electronic mail including important information requiring secrecy such as customer information and product information, the mail has been distinguished from the other electronic mails, for example, by attaching an identifier depicting the importance of the electronic mail to the subject.
When a customer gives an instruction to delete the electronic mail including important information, the electronic mail to be deleted is handled according to the identifier attached to the subject and deleted manually. Further, when the electronic mail to be deleted has been sent to another user, the user is ordered to delete the electronic mail.
However, in recent years, the number of electronic mails managed by a user has been increasing and the work load of deleting the delete-ordered electronic mails and instructing a receiver to delete the above has been increasing. As a result, there is a problem when a user forgets to delete the electronic mail or a user forgets to instruct a receiver to delete it.